Continuous web printing allows economical, high-speed, high-volume print reproduction. In this type of printing, a continuous web of paper or other substrate material is fed past one or more printing subsystems that form images by applying one or more colorants onto the substrate surface. In a conventional web-fed rotary press, for example, a web substrate is fed through one or more impression cylinders that perform contact printing, transferring ink from an imaging roller onto the web in a continuous manner.
Proper registration of the substrate to the printing device is of considerable importance in print reproduction, particularly where multiple colors are used in four-color printing and similar applications. Conventional web transport systems in today's commercial offset printers address the problem of web registration with high-precision alignment of machine elements. Typical of conventional web handling subsystems are heavy frame structures, precision-designed components, and complex and costly alignment procedures for precisely adjusting substrate transport between components and subsystems.
The problem of maintaining precise and repeatable web registration and transport becomes even more acute with the development of high-resolution non-contact printing, such as high-volume inkjet printing. With this type of printing system, finely controlled dots of ink are rapidly and accurately propelled from the printhead onto the surface of the moving media, with the web substrate often coursing past the printhead at speeds measured in hundreds of feet per minute. No impression roller is used; synchronization and timing are employed to determine the sequencing of colorant application to the moving media. With dot resolution of 600 dots-per-inch (DPI) and better, a high degree of registration accuracy is needed.
One factor for maintaining registration accuracy relates to the mounting and alignment of the printer components that apply the ink or other liquid onto the rapidly moving medium. Temperature effects, for example, can compromise registration as materials having different Coefficients of Thermal Expansion (CTEs) expand or contract at different rates. One temperature concern for inkjet printers relates to the need for drying equipment at one or more positions along the paper path. Heat that is generated for drying the media is concentrated over small portions of the printer system, creating potential localized hot-spots, with changing temperature gradients during printer operation.
With the increased size and complexity of a large-scale, continuous web printing system, conventional solutions for printhead registration and alignment fall far short of what is needed. This problem becomes particularly significant when considering practical concerns such as system assembly procedures, scalability of the system, the need for repair, replacement, or reconfiguration in the field, and variable ambient temperatures and other environmental factors for printing systems. It would be advantageous, for example, to allow system reconfiguration or repair without requiring excessive cost and time for maintaining alignment of printer components along the paper path.
Thus, there is a need for a printing system that provides alignment of printer components relative to each other or to other aspects of the printing system, for example, a moving media web, without the requiring complex or costly alignment and adjustment procedures and without imposing constraints on the environment in which the printing system is used.